A336387 Number of prime divisors of n that do not divide sigma(n); a(1) = 0.

0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 0, 2, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 0, 1, 2, 1, 2, 1, 1, 1, 1, 2

Offset

1,21

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for sequences related to sigma(n)

Formula

a(n) = Sum_{p over distinct primes dividing n} [sigma(n) != 0 mod p].

Mathematica

Table[Length[Select[FactorInteger[n][[All, 1]], Mod[DivisorSigma[ 1, n], #]!= 0&]], {n, 110}] (* Harvey P. Dale, Jan 15 2022 *)

Prog

(PARI) A336387(n) = if(1==n, 0, my(s=sigma(n)); #select(p -> (s%p), factor(n)[, 1]));

Crossrefs

Cf. A175200 (positions of zeros).

Cf. also A173438, A336352, A336388.

Sequence in context: A341969 A261447 A287325 * A358217 A286133 A328248

Adjacent sequences: A336384 A336385 A336386 * A336388 A336389 A336390

Keyword

nonn

Author

Antti Karttunen, Jul 25 2020

Status

approved